As much as I would like to fight the idea, the sun has huge impact on the mood of almost everyone. Not only each person isolated quits the resignation mood from clouds and grey skies, but the collective mood creates a synergy with every person process, accelerating change and bringing consequences as more laughs, less stress, equilibrium, motivation an at least superficially happiness.
In the process of generating happiness only from the inside, I would love to isolate external factors, but I have to accept the sun helps, and helps a lot. I suppose we as animals can’t avoid influences from the environment. Welcome again sunny days!!